The present invention relates generally to outdoor enclosures for electronic components and, more particularly, to an outdoor enclosure for electronic components that uses passive heating and cooling to control the temperature of the enclosure.
When telecommunications equipment is deployed in outdoor locations, a cabinet or enclosure protects the electronics from weather and environmental contaminants. The reliability of electronic components decreases significantly if they are subjected to high temperature extremes, especially if the temperature swings or cycles are frequent. The temperature swings may be due to heat generated by the electronics (i.e., more heat is produced at peak times), natural temperature variations, and solar loading. To protect the electronics equipment, various methods are used to control the internal temperature of the electronics enclosure.
Ventilated cabinets are sometimes used to cool electronics equipment inside an enclosure or cabinet. Ventilated cabinets use natural or forced convection to draw ambient air through the cabinet to cool the equipment inside the cabinet. Ventilated cabinets are relatively inexpensive and require little maintenance. However, the electronics inside the ventilated cabinet are exposed to the air flow, which may contain environmental contaminants, such as moisture, nitrates, hydrocarbons, sulfur dioxide, nitrogen oxides, hydrogen sulfides, chlorine, ozone, salt, and the like.
Sealed cabinets provide an alternative to ventilated cabinets where environmental contamination is a concern. Sealed cabinets use heating and cooling systems to maintain the electronics in the cabinet within the desired temperature range without exposing the electronics to potentially harmful contaminants. The heating and cooling systems include fans, air conditioners, and heaters, which consume space in the cabinet and add considerably to the cost of the cabinet. Additionally, such components require periodic maintenance to maintain them in proper operating condition.
Passive cooling methods for cooling electronics enclosures are also known. Passive cooling relies on conduction and radiation to passively cool the electronics equipment inside an enclosure without fans, air conditioners, or heat exchangers. Passive cooling of electronics enclosures is less expensive than active cooling systems, reduces energy consumption, and minimizes noise. Additionally, because there are fewer components to fail, passive cooling systems are generally more reliable and robust than active cooling systems.
Passive cooling systems for electronics enclosures dissipate heat generated by the electronics through natural convection and radiation. However, if the enclosure is placed in direct sunlight, the solar load on the cabinet may be as many more times that of the heating load of the electronics. In order to dissipate heat generated by the solar load using passive methods, a phase change material (PCM) is typically used. Phase change materials are materials that change state (e.g., from solid to liquid and vice versa) as the temperature changes. The temperature at which the PCM changes state is referred to as the phase change temperature. As heat builds up in the enclosure, the PCM begins to change from solid to liquid when the temperature inside the enclosure reaches the phase change temperature. While the phase change is occurring, the PCM continues to absorb heat while the temperature remains the same. The temperature does not begin to increase again until the PCM has changed phase. The amount of heat, or energy, required to change the PCM from one phase to another is called the latent heat of the PCM. Conversely, when the solar load is removed and the temperature inside the enclosure begins to cool, the temperature of the PCM also reduces and it changes back to a solid state.
The present invention relates generally to a passively-cooled electronics enclosure for use outdoors. The electronics enclosure comprises an electronics cabinet or housing, a mounting bracket for mounting the electronics housing to a support structure, and a heat absorption module. The electronics housing may be directly mounted to the mounting bracket or, alternatively, may be mounted to the heat absorption module which, in turn, mounts to the mounting bracket. Thus, the electronics housing may be used with or without the heat absorption module. When the electronics enclosure is deployed in a location where it is not exposed to direct sunlight, it may be used without a heat absorption module. Conversely, when the electronics enclosure is deployed in a location where it is subjected to solar loading, the heat absorption module may be used to passively cool the electronics housing.